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    <title>Document</title>
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<body>
    
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<script>
    //创建数组并赋值
    let arr = [23,566,21,542,78];
    console.log(arr[2]);//21
    let arr2 = ['tom',34,4,true,,];//可以有不同的数据类型
    console.log(arr2[4]);//undefined
    arr2[4] = null;
    console.log(arr2[4]);
    console.log('------------------');
    //遍历数组
    console.log(arr.length);//获取数组长度
    for(let i = 0;i<arr.length;i++){
        console.log(arr[i]);
    }
    console.log('-------------------------');
    //找出数组score中的最大值，并计算出这个数组的平均值
    //score = [89,67,59,90,54,77,83,88.5,43,10,68]
    let score = [89,67,59,90,54,77,83,88.5,43,10,68];
    let max = score[0];
    let sum = 0;
     for(let a = 0; a<score.length; a++){
        if(score[a]>max){
            max=score[a];
        }
        sum += score[a];
    }
    let avg = sum/score.length;
    console.log('最大值是：'+max);
    console.log('平均分：'+avg);
    console.log('_________');
    score[1000] = 88;
    console.log(score[1000]);
    console.log(score.length);
    for(let i=0;i<score.length;i++){
        console.log(score[i]);
    }
    delete score[1000];
    console.log(score[1000]);
</script>
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